This invention relates to an ink jet printer, an ink jet head unit, and an image forming method which makes image formation on a recording medium by the jetting of ink drops on the recording medium.
In recent years, as an image forming method capable of forming an image simply at a low cost, an image forming method using an ink jet printer is used in a large number of cases. A serial type ink jet printer moves a recording medium, a paper sheet for example, intermittently in the sub-scanning direction, and while the recording medium is stopped, moves the head over the recording medium in the main scanning direction which is perpendicular to the sub-scanning direction. Further, during the moving of the head in the main scanning direction, the ink jet printer jets ink drops from the head to the recording medium by deforming a piezoelectric element forming an ink chamber, or by heating a heater in the case where a heater is provided in the ink chamber. In another case, an ink jet printer having a line-shaped head moves a recording medium, a paper sheet for example, in the sub-scanning direction, and jets ink drops from the line-shaped head provided lengthwise in the main scanning direction which is perpendicular to the sub-scanning direction to the recording medium. The methods of jetting ink drops in this case are same as those of serial type ink jet printer. By such operations of ink jet printers, an image is formed on a recording medium.
Incidentally, as regards an ink to be used in an ink jet printer, there is an active-ray-setting ink to be hardened by the irradiation of active rays such as ultraviolet rays or electronic rays. An active-ray-setting ink is composed of, for example, a color material, a polymerizable monomer or oligomer, and a polymerization initiator and a polymerization accelerator at need, and is hardened by a bridging reaction or a polymerization reaction induced by the irradiation of active rays. A printer practicing image formation with such an active-ray-setting ink has been being remarked in recent years from the viewpoint that it gives out comparatively lower smell compared to a printer practicing image formation with a solvent ink and is capable of recording on a recording medium having no ink absorbing ability.
Incidentally, as an ink jet printer making a print with a UV ink to be hardened by ultraviolet rays, such one as shown in FIG. 9 is known. FIG. 9 shows the top view of a state in which a recording medium 104 is being transported in the sub-scanning direction B as an outline view for the purpose of making it easy to understand the layout of the ink jet head. In the ink jet printer shown in FIG. 9, each of the heads 102, 102, - - - jets ink drops of a UV ink to the recording medium 104; the heads 102, 102, - - - are provided on the carriage 101 which is movable back and forth in the main scanning direction A, and a light source 103 is provided at the downstream side of the carriage 101 in the sub-scanning direction B. That is, the light source 103 is provided at the downstream position in the transporting direction Bxe2x80x2 of the recording medium 104.
This ink jet printer jets ink drops during the moving of the carriage 101 in the main scanning direction A from the heads 102, 102, - - - towards the recording medium 104, transports the recording medium 104 in the direction of the sub-scanning direction B, and makes the light source 103 emit ultraviolet rays. By this operation, ink drops landed on the recording medium 104 are hardened. However, in this ink jet printer, because it takes a considerable time to emit ultraviolet rays after the ink drops are landed on the recording medium 104, the ink drops landed spread to an extent greater than necessary on the recording medium.
Especially, in the case of color printer, where plural heads jet respectively different color ink to form a color image, difference in the degree of color mixture occurs and may lead to a large image problem.
For the purpose of obtaining a high-quality image, it is desirable to irradiate the ink drops by ultraviolet rays to harden the ink drops as soon as possible after the UV ink drops are landed on the recording medium.
Therefore, the object of this invention is to make it possible to form a high-quality image on a recording medium. That is, the object is to accomplish an image formation of high image quality by the controlling of the spreading of ink drops landed on the recording medium as well as by the equalizing of the degree of their spreading.
The above-mentioned object is accomplished by any one of the structures described below.
(1) An ink jet printer for forming an image on a recording medium with an active-ray-setting ink, which is hardened by an irradiation of active rays, comprising: a plurality of heads, each of the plurality of heads having a plurality of jet openings for jetting the active-ray-setting ink as ink drops towards the recording medium; and a plurality of active ray sources to irradiate active rays for hardening the ink drops of the active-ray-setting ink landed on the recording medium, wherein each of the plurality of heads and each of the plurality of active ray sources are arranged alternately.
According to the structure (1), because each of the plural heads and each of the plural active ray sources are arranged alternately, the ink drops landed on a recording medium, from whichever heads they have been jetted, are immediately irradiated by the active rays emitted from the neighboring active ray source. Hence, any ink drop jetted from any one of the heads starts setting by the irradiation of the active rays within a specified range of time after landing on the recording medium; therefore, ink drops do not spread on the recording medium, and what is called a blur is prevented. Further, because the time interval from the landing of an ink drop to the irradiation by active rays does not vary from an ink drop from one head to that from another, the dispersion of the blur among the heads can be suppressed. Thus, a high-quality image can be obtained.
(2) An ink jet printer as set forth in the structure (1) further comprising a mobile body being movable in the main scanning direction relatively to a recording medium and having the aforesaid plural heads and the aforesaid plural active ray sources arranged alternately in said main scanning direction.
According to the structure (2), because the plural heads and the plural active ray sources are provided in the mobile body being movable in the main scanning direction relatively to a recording medium, this structure can be applied to an ink jet printer having a mechanism such that the printer jets ink drops to a recording medium while it moves the heads in the main scanning direction. This structure can provide a serial type ink jet printer.
(3) An ink jet printer as set forth in the structure (2), wherein the aforesaid plural jet openings are formed linearly along the sub-scanning direction which is substantially perpendicular to the aforesaid main scanning direction.
According to the structure (3), because the plural jet openings are formed linearly along the sub-scanning direction, compared to a conventional technology shown in FIG. 9, the time interval from the landing of an ink drop on a recording medium to the irradiation by active rays becomes shorter. Thus, the spreading of ink drops is reduced.
(4) The ink jet printer of the structure (2), wherein the intervals between each of the plurality of heads and each of the active ray sources neighboring to said each of the plurality of heads become equal to one another.
According to the structure (4), since the intervals between each of the plurality of heads and each of the active ray sources neighboring to said each of the plurality of heads become equal to one another, any one of ink drops jetted from any one of the heads has approximately a definite time interval from the landing on a recording medium to the irradiation by active rays. And all the ink drops have approximately a definite degree of spreading on the recording medium; thus a higher image quality can be obtained.
(5) An ink jet printer as set forth in the structure (2), wherein the aforesaid plural active ray sources are arranged in such a way that the intervals between two neighboring active ray sources become equal to one another, the aforesaid plural heads are arranged in such a way that the intervals between two neighboring heads become equal to one another, and the aforesaid mobile body is controlled so as to move at a constant speed in the range of image formation.
According to the structure (5), because the intervals between two neighboring active ray sources and the intervals between two neighboring heads both fall within a specified distance, and the mobile body moves at a constant speed in the range of image formation, any one of ink drops jetted from any one of the heads has approximately a definite time interval from the landing on a recording medium to the irradiation by active rays. Thus, although there is a little difference depending on the position of the jet openings of the heads, the time required for hardening becomes equalized approximately, and all the ink drops have approximately a definite degree of spreading on the recording medium; thus a higher image quality can be obtained.
(6) An ink jet printer as set forth in the structure (2), wherein said ink jet printer is controlled so as to jet ink drops from the aforesaid jet openings and emit the aforesaid active rays during the movement of the aforesaid mobile body.
According to the structure (6), an ink drop landed on a recording medium is irradiated by active rays from an active ray source immediately after the landing. Hence, the ink drop does not spread on the recording medium, and what is called a blur is prevented; thus, a high-quality image can be obtained.
(7) An ink jet printer as set forth in the structure (1), wherein the aforesaid plural heads and the aforesaid plural active ray sources are alternately arranged in the sub-scanning direction relatively to a recording medium.
According to the structure (7), this invention can be applied to an ink jet printer having a head of the same length as the length in the main scanning direction of a recording medium, what is called a line head.
(8) An ink jet printer as set forth in the structure (7), wherein the aforesaid plural jet openings are formed linearly along the main scanning direction which is substantially perpendicular to the aforesaid sub-scanning direction.
According to the structure (8), because the plural jet openings are formed linearly along the main scanning direction, in an ink jet printer using what is called a line head, the time interval from the landing of an ink drop to the irradiation by active rays becomes short. Thus, the spreading of ink drops is reduced.
(9) The ink jet printer of the structure (7), wherein the intervals between each of the plurality of heads and each of the active ray sources neighboring to said each of the plurality of heads become equal to one another.
According to the structure (9), since the intervals between each of the plurality of heads and each of the active ray sources neighboring to said each of the plurality of heads become equal to one another, any one of ink drops jetted from any one of the heads has approximately a definite time interval from the landing on a recording medium to the irradiation by active rays. And all the ink drops have approximately a definite degree of spreading on the recording medium; thus a higher image quality can be obtained.
(10) An ink jet printer as set forth in the structure (7), wherein the aforesaid plural active ray sources are arranged to have equal intervals between two neighboring active ray sources, and the aforesaid plural heads are arranged to have equal intervals between two neighboring heads.
According to the structure (10), because the intervals between two neighboring active ray sources and the intervals between two neighboring heads both fall within a specified distance, for an ink drop jetted from any one of the heads of what is called a line head type, the time interval from the landing of an ink drop on a recording medium to the irradiation by active rays becomes approximately constant. Thus, the time required for hardening is made approximately equalized, and any ink drop has approximately a definite degree of spreading on a recording medium; thus, a higher image quality can be obtained.
(11) An ink jet printer as set forth in the structure (1), wherein the time interval from the landing of an ink drop which is jetted from any one of the aforesaid plural heads to the irradiation by active rays emitted at first by any one of the aforesaid active ray sources, from whichever head the ink drop is jetted, falls within a specified range of time.
According to the structure (11), for ink drops, from whichever head they are jetted, because the dispersion of the time up to the irradiation by active rays becomes small, the degree of spreading of the ink drops on a recording medium becomes approximately equal to one another, and the degree of what is called a blur becomes approximately constant; thus, a high-quality image can be obtained.
(12) The ink jet printer of the structure (1), further comprising a transporting mechanism for transporting the recording medium in a sub-scanning direction.
According to the structure (12), it becomes possible to form an image on the recording medium by transporting the recording medium.
(13) The ink jet printer of the structure (1), wherein the plurality of heads are heads for forming a full color image.
According to the structure (13), since unevenness and blur of each color ink can be prevented in the course of color image forming, a high quality full color image without undesired color mixing can be obtained.
(14) An ink jet printer for forming an image on a recording medium with an active-ray-setting ink which is hardened by the irradiation of the active rays comprising
a mobile body being movable in the main scanning direction relatively to a recording medium,
an active ray source provided on said mobile body for applying said active rays to a recording medium, and
a plurality of lines of jet openings, each line having a plurality of jet openings, arranged at both the sides of said active ray source in said main scanning direction for jetting said active-ray-setting ink as ink drops towards a recording medium.
According to the structure (14), because a line of jet openings is arranged at each of both sides of the active ray source, in the case when this invention is applied to an ink jet printer of a type such that the printer jets ink drops at the time of moving forward and at the time of moving backward, for an ink drop jetted at either of both the times, hardening begins by the irradiation of active rays within a specified range of time after the landing. Hence, independently of the time of jetting, the spreading of ink drops on a recording medium can be suppressed, and what is called a blur can be prevented; thus, a high-quality image can be obtained.
(15) An ink jet head comprising: a plurality of lines of jet openings, each line having a plurality of jet openings, arranged linearly on different lines respectively for jetting an active-ray-setting ink which is hardened by the irradiation of active rays as ink drops, and an active ray source provided between said plurality of lines of jet openings for emitting active rays.
According to the structure (15), if this ink jet head is applied to an ink jet printer, because an ink drop landed on a recording medium is irradiated by active rays immediately after the landing, a high-quality image can be obtained.
(16) An image forming method for forming an image on a recording medium with an active-ray-setting ink, which is hardened by an irradiation of active rays, comprising:
jetting the active-ray-setting ink as ink drops from a plurality of heads towards the recording medium; and
irradiating ink drops landed on the recording medium with the active rays, after the jetting process,
wherein the time interval after an ink drop is landed on the recording medium by the jetting process up to the time the ink drop is irradiated by the active rays in the irradiating process is approximately the same for the ink drop jetted from any of the plurality of heads.
According to the structure (16), since the intervals between each of the plurality of heads and each of the active ray sources neighboring to said each of the plurality of heads become equal to one another, any one of ink drops jetted from any one of the heads has approximately a definite time interval from the landing on a recording medium to the irradiation by active rays. And all the ink drops have approximately a definite degree of spreading on the recording medium; thus a higher image quality can be obtained.
(17) The image forming method of the structure (16), wherein the time interval after an ink drop is landed on the recording medium by the jetting process up to the time the ink drop is irradiated by the active rays in the irradiating process is controlled to become 0.001 second to 0.4 second for the ink drop jetted from any of the plurality of heads.
According to the structure (17), because an ink drop landed on a recording medium is immediately irradiated by active rays, the spreading of ink drops on a recording medium can be suppressed, and the blur of ink can be prevented. Hence, a high-quality image can be obtained.
(18) The image forming method of the structure (17), wherein the time interval after an ink drop is landed on the recording medium by the jetting process up to the time the ink drop is irradiated by the active rays in the irradiating process is controlled to become 0.005 second to 0.2 second for the ink drop jetted from any of the plurality of heads.
According to the structure (18), because the spreading of ink drops on a recording medium can be suppressed more sufficiently, the blur of ink can be better prevented. Hence, a higher-quality image can be obtained. On the other hand, because the allowance for the lower limit value is broadened, the degree of freedom in an image forming process is made greater.
Further, the above-mentioned object can be accomplished by any one of the structures shown below.
(101) An ink jet printer for forming an image on a recording medium by jetting active-ray-setting ink drops to be hardened by the irradiation of active rays to a recording medium, comprising
a mobile body being movable in the main scanning direction relatively to a recording medium,
one or a plurality of heads provided on said mobile body having a plurality of jet openings for jetting an active-ray-setting ink as ink drops towards a recording medium, and
one or a plurality of active ray sources for emitting active rays towards a recording medium, characterized by
said active ray sources being arranged alternately with said heads in the main scanning direction.
According to the structure (101), one or a plurality of heads are provided on a mobile body, and from the jet openings of each head, ink drops of an active-ray-setting ink are jetted. Because a plurality of active ray sources are arranged alternately for the heads with respect to the main scanning direction, an ink drop landed on a recording medium, from a jet opening of whichever head it has been jetted, accompanied by the movement of the mobile body, is immediately irradiated by active rays from the active ray source adjacent to the head of jetting source. Hence, an ink drop jetted from a jet opening of any one of the heads is irradiated by active rays within a specified range of time after it is landed on a recording medium, to start to be hardened; therefore, ink drops do not spread on a recording medium, and what is called a blur can be prevented. Thus, this invention exhibits an effect to make it possible to obtain a high-quality image.
Further, because a plurality of active ray sources and a plurality of heads are alternately arranged in the main scanning direction, the time interval after an ink drop jetted from one head is landed on a recording medium up to the time it is irradiated by the active rays from the neighboring active ray source is approximately equal to the time interval after an ink drop jetted from another head is landed on the recording medium up to the time it is irradiated by active rays from the neighboring active ray source. Further, compared to a conventional example shown in FIG. 9, because the time interval from the landing of an ink drop up to the irradiation by active rays becomes shorter, the blur of ink drops is reduced. Hence, this invention exhibits an effect to make it possible to obtain a higher-quality image.
In addition, the term xe2x80x9cheadxe2x80x9d stands for a combination of jet openings (a group of jet openings) having a plurality of them.
(102) An ink jet printer as set forth in the structure (101), characterized by the aforesaid jet openings being formed linearly along the sub-scanning direction which is substantially perpendicular to the aforesaid main scanning direction in the aforesaid one or a plurality of heads.
In the structure (102), because a plurality of jet openings arranged linearly along the sub-scanning direction in a head, compared to a conventional one shown in FIG. 9, the time interval from the landing of an ink drop up to the irradiation by active rays becomes shorter; therefore, the blur of ink drops is reduced. Further, the length of the head in the main scanning direction is reduced shorter than the structure (1), the blur of ink drops is more reduced. Hence, this invention exhibits an effect to make it possible to obtain a higher-quality image.
(103), An ink jet printer as set forth in the structure (101) or (102) characterized by it that the intervals between neighboring two of the aforesaid active ray sources are all equal to one another, and the intervals between neighboring two of the aforesaid heads are all equal to one another, and the aforesaid mobile body moves at a constant speed in the image formation range.
According to the structure (103), the intervals between two neighboring active ray sources are all equal to one another, and the intervals between two neighboring heads are all equal to one another, the distance from one to the other of any combination of an active ray source and a head neighboring to each other falls within a specified range, and the mobile body moves at a constant speed; therefore, for jetted ink drops, from whichever jet opening they are jetted, the time interval from the landing to the irradiation is approximately constant. Hence, landed ink drops, from whichever head they are jetted, have approximately the same degree of spreading. Further, compared to the conventional example shown in FIG. 9, for an ink drop, the time interval from the landing to the irradiation by active rays becomes shorter; therefore, the blur of the ink drop is reduced. Further, the length of the heads in the main scanning direction becomes shorter than that of the structure (101), the blur of ink drops is more reduced. Hence, this invention exhibits an effect to make it possible to obtain a higher-quality image.
(104) An ink jet printer as set forth in the structure (101), characterized by it that the time interval from the landing of an ink drop jetted from a head on a recording medium to the irradiation by the active rays emitted from the neighboring active ray source located at the rear side in the direction of said head moving in the main scanning direction with the movement of the aforesaid mobile body falls within a range of time for a jet opening of any head.
In the structure (104), compared to the conventional example shown in FIG. 9, for an ink drop, the time interval from the landing to the irradiation by active rays becomes shorter; therefore, the blur of the ink drop is reduced. Further, the length of the heads in the main scanning direction becomes shorter than that of the structure (101), the blur of ink drops is more reduced. Hence, this invention exhibits an effect to make it possible to obtain a higher-quality image.
(105) An ink jet printer as set forth in any one of the structures (101) to (104), characterized by it that an image is formed in such a way that ink drops are jetted from the aforesaid jet openings during the movement of the aforesaid mobile body.
In the structure (105), because ink drops are jetted from the jet openings during the movement of the mobile body, the ink drops landed on a recording medium are irradiated by the active rays from the active ray source immediately after the jetting. Hence, the ink drops do not spread on the recording medium, and what is called a blur is prevented. Thus, this invention exhibits an effect to make it possible to obtain a high-quality image.
(106) An ink jet printer for forming an image on a recording medium by jetting active-ray-setting ink drops to be hardened by the irradiation of active rays to a recording medium, characterized by it that
an active ray source for applying active rays for setting to ink drops is provided on a mobile body to be moved in the main scanning direction relatively to a recording medium, and
a line of jet openings for jetting an active-ray-setting ink as ink drops towards a recording medium is provided at either of the sides of said active ray source.
In the structure (106), because a line of jet openings is provided at either of the sides of the active ray source, an ink drop, from a jet opening of whichever head it is jetted, is immediately irradiated by the active rays from the active ray source, accompanied by the movement of the mobile body. Hence, an ink drop jetted from a jet opening of any head is irradiated by active rays within a specified range of time after it is landed on a recording medium to start setting; therefore, ink drops do not spread on the recording medium, and what is called a blur is prevented. Thus, this invention exhibits an effect to make it possible to obtain a high-quality image.
(107) An ink jet head comprising
jet openings arranged linearly for jetting an active-ray-setting ink to be hardened by the irradiation of active rays as ink drops towards a recording medium, and
an active ray source for emitting active rays towards a recording medium, characterized by it that
as regards said jet openings linearly arranged, a plurality of them are formed, and said active ray source is disposed between a line of said jet openings and the neighboring one.
In the structure (107), because an active ray source is disposed between a line of said jet openings and the neighboring one, ink drops jetted are irradiated immediately after the landing on a recording medium by the active rays from the active ray source. Thus, this invention exhibits an effect to make it possible to obtain a high-quality image.
(108) An image forming method comprising
a jetting process for jetting active-ray-setting ink drops to be hardened by the irradiation of active rays as ink drops to a recording medium, and
an irradiation process for irradiating ink drops landed on a recording medium by active rays, characterized by the time interval from the jetting of an ink drop to the irradiation being controlled so as to fall within a range of 0.0001 second to 0.4 second.
(109) An image forming method as set forth in the structure (108), characterized by the time interval from the jetting of an ink drop to the irradiation being controlled desirably so as to fall within a range of 0.0005 second to 0.2 second.